Flexible printed circuit board

ABSTRACT

There is provided a flexible printed circuit board. The flexible printed circuit board includes: a flexible insulation layer having a first surface and a second surface; a first land which is conductive and which is provided on the first surface of the flexible insulation layer; and a conductive member which is provided on the second surface of the flexible insulation layer. A recess is formed on the first land.

CROSS REFERENCE TO RELATED APPLICATION

This is a Division of application Ser. No. 14/815,413 filed Jul. 31,2015, which claims priority from Japanese Patent Application No.2014-159097 filed on Aug. 4, 2014, and titled “ FLEXIBLE PRINTED CIRCUITBOARD”, the disclosure of which is incorporated herein by reference inits entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present teaching relates to a flexible printed circuit board whichcan be electrically connected to a counterpart electrode reliably.

Description of the Related Art

For example, a strain gage measuring the strain or distortion of astructure is formed in one flexible printed circuit board (a firstflexible printed circuit board) which is very thin. In order to extractor take out the output from the strain gage, another flexible printedcircuit board (a second flexible printed circuit board) for transmittinga signal is joined to the first flexible printed circuit board withsoldering so that the electrode of the first flexible printed circuitboard is electrically connected to the counterpart electrode of thesecond flexible printed circuit board.

The technology for joining the electrode of the first flexible printedcircuit board to the counterpart electrode of the second flexibleprinted circuit board with soldering is generally known and isdisclosed, for example, in Japanese Patent Application Laid-open No.2006-303354 and Japanese Utility Model Publication No. H5-29178.

SUMMARY

The lands of solder joints of the flexible printed circuit boardsdescribed in Japanese Patent Application Laid-open No. 2006-303354 andJapanese Utility Model Publication No. H5-29178 have no specialstructure for allowing air to escape outside at the time ofthermocompression bonding. Thus, air could remain in the solder jointsat the time of thermocompression bonding and cause the detachment orexfoliation of the solder joints. Specifically, when pre-solder(pre-tin) is melted so that the through holes are filled with thepre-solder, the air in the through holes is not allowed to escape. Thisforms a layer of air between copper foil and solder to cause thedetachment or exfoliation of the solder joints.

An object of the present teaching is to provide a flexible printedcircuit board having an electrode, which is connected or joined to acounterpart electrode via a solder joint with sufficient strength so asto provide satisfactory conductivity for a long time.

According to a first aspect related to the present teaching, there isprovided a flexible printed circuit board including: a flexibleinsulation layer having a first surface and a second surface; a firstland which is conductive and which is provided on the first surface ofthe flexible insulation layer; and a conductive member which is providedon the second surface of the flexible insulation layer, wherein a recessis formed on the first land.

According to a second aspect related to the present teaching, there isprovided a flexible printed circuit board including: an insulation layerwhich has a first surface and a second surface, and through which anthrough hole connecting the first surface and the second surface areformed, a metallic first land provided around an opening, on the firstsurface of the insulation layer, defined by the through hole; a metallicsecond land provided around an opening, on the second surface of theinsulation layer, defined by the through hole; a metallic connectingportion provided in the through hole to connect the first land and thesecond land, wherein a channel which connects the through hole and anoutside of the first land are formed at a position lower than a top ofthe first land.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a flexible printed circuit board relatedto an embodiment of the present teaching as viewed from the side of oneof lands provided in the flexible printed circuit board.

FIG. 2 is a perspective view depicting a counterpart electrode to beconnected to the flexible printed circuit board depicted in FIG. 1 withsoldering.

FIG. 3 is an illustrative view of a welding process depicting thecross-section taken along the line III-III in FIG. 1 and depicting astate immediately before the electrode of the flexible printed circuitboard depicted in FIG. 1 is joined or connected to the counterpartelectrode depicted in FIG. 2 with soldering.

FIG. 4 is an illustrative view of the welding process depicting a state,subsequent to the state depicted in FIG. 3, in which the flexibleprinted circuit board depicted in FIG. 1 is completely pressed againstthe counterpart electrode with a pulse heater.

FIG. 5 is a plan view depicting an exemplary flexible printed circuitboard, which has lands each corresponding to the land depicted in FIG.1.

FIG. 6A is a perspective view of the shape of the land related to theembodiment of the present teaching, and FIG. 6B is a perspective view ofthe shape of a land related to a modified embodiment of the presentteaching.

FIG. 7 is a bottom view of a flexible printed circuit board related to amodified embodiment of the present teaching.

FIG. 8 is a cross-sectional view taken along the line VIII-VIII in FIG.7.

DESCRIPTION OF THE EMBODIMENTS

In the following, an explanation will be made with reference to thedrawings about a flexible printed circuit board 1 related to anembodiment of the present teaching. FIG. 1 is a perspective view of theflexible printed circuit board 1 related to the embodiment of thepresent teaching as viewed from the side of one of lands (heating sideland 130) of an electrode provided in the flexible printed circuit board1. FIG. 2 is a perspective view depicting a counterpart electrode to beconnected to the flexible printed circuit board 1 depicted in FIG. 1with soldering. FIGS. 3 and 4 are illustrative views chronologicallyillustrating states that the flexible printed circuit board 1 related tothis embodiment is crimped or pressure welded to a part of anotherflexible printed circuit board having the counterpart electrode throughthermocompression bonding.

In the drawings, the sizes, thicknesses, and dimensions of components orparts related to the embodiment and modified embodiments are depictedexaggeratedly for easy understanding of the present teaching.

As depicted in FIGS. 3 and 4, the flexible printed circuit board 1related to this embodiment includes a flexible insulation layer 11, aheating side land 130, and a conductor pattern 12. The insulation layer11 is made of polyimide (PI). The heating side land 130 (a first land)is formed on the upper surface (one surface) (a first surface) of theinsulation layer 11. The conductor pattern 12 is formed on the lowersurface (the other surface) (a second surface) of the insulation layer11. The conductor pattern 12 is electrically connected with the heatingside land 130 via a through hole 140. The conductor pattern 12 is madeof rolled copper foil and includes a welding side land 120, a thin wirepattern for electrical connection 125 (wiring), and an insulatingcoating 129. The welding side land 120 has a circular or annular shape.The thin wire pattern for electrical connection 125 extends from thewelding side land 120 along the insulation layer 11. The insulatingcoating 129 covers the entire flexible printed circuit board 1 exceptfor the welding side land 120 and the part, of the thin wire pattern forelectrical connection 125, required for electrical connection with thecounterpart electrode.

As depicted in FIGS. 1 and 6A, the heating side land 130 has a circularplate shape or disk shape in plan view (hereinafter referred to as“disk”). The heating side land 130 is composed of two pieces of rolledcopper foil and a groove 131 (slit). The two pieces of rolled copperfoil are disposed to face each other with a small space interveningtherebetween, and each piece has a substantially semicircular shape inplan view (hereinafter referred to as “semicircular plate”). The groove131 is sandwiched by the two pieces of rolled copper foil. That is, thegroove 131 is formed as one exemplary aspect of a recess of the heatingside land 130 (The groove 131 is an example of recess formed in the landrelated to the present teaching). The heating side land 130 is formed onthe upper surface of the insulation layer 11 to be concentric, in planview, with the welding side land 120. The heating side land 130 iselectrically connected with the welding side land 120 via a rolledcopper foil 141 covering the inner circumferential surface of thethrough hole 140. That is, the heating side land 130 and the weldingside land 120 are electrically and thermally connected with each othervia the rolled copper foil 141 (a metallic connecting portion) in thethrough hole 140. Note that, in this specification, the expression of“thermally connected” mean a state that objects are connected with ametallic material, such as copper, having good thermal conductivity.

Subsequently, an explanation will be made about a structure of acounterpart electrode 220 to which the flexible printed circuit board 1is connected. In this embodiment, the counterpart electrode 220 depictedin FIG. 2 is provided at an end of a flexible printed circuit board 20having a strain gage (not depicted in FIG. 2). The end of the flexibleprinted circuit board 20 includes a base 21, a gage side conductorpattern 22, pre-solder 230, and a cover glass 25. The gage sideconductor pattern 22 is provided on the upper surface of the base 21 andit is made of rolled copper foil. The pre-solder 230 is provided on awide surface of an end of the gage side conductor pattern 22 to rise orbulge slightly. The cover glass 25 covers the base 21, except for aportion at which the pre-solder 230 is formed to rise or bulge, in orderto protect the gage side conductor pattern 22.

Subsequently, an explanation will be given about a process for bondingthe pre-solder 230 on the gage side conductor pattern 22 to the weldingside land 120 of the flexible printed circuit board 1 withthermalcompression-bonding. FIGS. 3 and 4 are illustrative views of awelding process. FIG. 3 depicts a state immediately before the electrodeof the flexible printed circuit board 1 is joined or connected to thecounterpart electrode 220 with soldering by the cross-section takenalong the line III-III in FIG. 1. FIG. 4 depicts a state subsequent tothe state depicted in FIG. 3, that is the state in which the flexibleprinted circuit board 1 is completely pressed against the counterpartelectrode 220 with a pulse heater H.

When the welding side land 120 of the flexible printed circuit board 1is welded to the counterpart electrode 220 via soldering, first, thelower side opening (the opening defined on the lower surface of theinsulation layer 11) of the through hole 140 of the flexible printedcircuit board 1 is allowed to approach the upper part of the pre-solder230 on the counterpart electrode 220 of the gage side conductor pattern22, and positional adjustment thereof is performed, as depicted in FIG.3. Next, the pulse heater H is moved downward in a state that the lowersurface (a heating surface) thereof is pressed against the upper surface(a contact surface) of the heating side land 130 of the flexible printedcircuit board 1. Pressing the pulse heater H against the upper surfaceof the heating side land 130 allows the heat of the pulse heater H to beconducted to the welding side land 120 of the flexible printed circuitboard 1 via the rolled copper foil 141 covering the innercircumferential surface of the through hole 140. Subsequently, when thepulse heater H is moved downward further, a part of the welding sideland 120 around the lower side opening of the flexible printed circuitboard 1 comes into contact with the pre-solder 230 and then it ispressed against thereto. This allows the heat from the pulse heater H tobe conducted to the pre-solder 230 so as to melt the pre-solder 230.

As depicted in FIG. 4, a part of melted solder 230A moves upward throughthe through hole 140 such that the through hole 140 is filled with themelted solder without void or cavity. In this situation, air in a spacedefined by the upper surface of the pre-solder 230, the lower surface ofthe pulse heater H, and the inner circumferential surface of the throughhole 140 is allowed to escape to the outside of the heating side land130 (released to the outside of the heating side land 130) via thegroove 131 of the heating side land 130 as the melted solder 230A movesupward. After the melted solder 230A has reached the lower surface ofthe pulse heater H, an excess solder 230B flows into the groove 131 ofthe heating side land 130 through the upper side opening (the openingdefined on the upper surface of the insulation layer 11) of the thoroughhole 140.

Next, the pulse heater H is moved away from the heating side land 130 tocool the melted solder 230A (including the excess solder 230B flowedinto the groove 131). Then, cooled solder is securely fixed to thewelding side land 120, the inner circumferential surface of the throughhole 140, and a part of or entire groove 131 of the heating side land130, of the flexible printed circuit board 1, and the counterpartelectrode 220 of the gage side conductor pattern 22. This results in thereliable electrical connection between the welding side land 120 and thecounterpart electrode 220 of the gage side conductor pattern 22.

Conventionally, there has been the following problem. That is, air inthe space defined by the upper surface of the pre-solder, the lowersurface of the pulse heater, and the inner circumferential surface ofthe through hole remains therein during the welding of pre-solder by theaid of the heat from the pulse heater. Thus, a layer of air is formedbetween the solder and the counterpart electrode of the gage sideconductor pattern and/or between the solder and the innercircumferential surface of the through hole. As a result, any failure ofsolder welding are caused, and consequently the conduction failurebetween the welding side land of one of the flexible printed circuitboards and the counterpart electrode of the other of the flexibleprinted circuit boards are caused. In this embodiment, however, sincethe flexible printed circuit board 1 has the above structure orconfiguration, the air in the space does not remain between the solderand the parts to which the solder is welded and the above problem can beavoided.

In addition to the above embodiment, as depicted in FIGS. 7 and 8, aportion of the thin wire pattern for electrical connection 125 (wiring)which is formed on the other surface of the flexible insulation layer 11and which is connected to the welding side land 120 may not be coveredwith the insulation coating (resist) 129, the portion having certainlength and being defined adjacent to the welding side land 120. The areawhich is not covered with the insulation coating 129 (the recess whichis obtained by the lack of the insulation coating 129 and has the depthcorresponding to the thickness of the insulation coating 129) may beused as a solder relief part (solder escape part) 132. When such solderrelief part 132 is provided, a part of excess solder flows into not onlythe groove 131 of the heating side land 130 of the flexible printedcircuit board 1 as described above but also the solder relief part 132,during the process in which the pre-solder 230 is melted by the pulseheater H. Accordingly, air is more reliably prevented from accumulatingbetween the solder and the parts to which the solder is welded.

FIG. 5 is a plan view depicting an exemplary flexible printed circuitboard 2 having a plurality of welding side lands 120 and a plurality ofheating side lands 130, the lands 120 and 130 corresponding to thosedepicted in FIG. 1. Although, the heating side lands 330 (each of whichis numbered with 331, 332, 333, 334, 335, and 336) having grooves,provided on the upper surface of the flexible printed circuit board 2have the same shape as that of the heating side land 130 in the aboveembodiment, it is characteristic that the heating side lands 330 aredisposed in a zigzag pattern along the width direction of the flexibleprinted circuit board 2 (the longitudinal direction in FIG. 5). Further,welding side lands 320 (each of which is numbered with 321, 322, 323,324, 325, and 326), which are conductor patterns and each have acircular shape in plan view, are formed on the lower surface of theflexible printed circuit board 2 at positions corresponding to theheating side lands 330 respectively. That is, the welding side lands 320are also disposed in the zigzag pattern along the width direction of theflexible printed circuit board 2 in a similar manner to the heating sidelands 330.

As clearly depicted in FIG. 5, the heating side lands 330 disposed inthe zigzag pattern and thin wire patterns for electrical connection 320a corresponding the heating side lands 330 are formed such that thelongitudinal direction (extending direction) of the grooves 131 formedin the heating side lands 330 is parallel with the extending directionof the thin wire patterns for electrical connection 320 a. In thepresent teaching, it is preferred that adjacent heating side lands 330,among the heating side lands 330 disposed in the zigzag pattern asdepicted in FIG. 5, have grooves 131 arranged such that extension linesextending in the longitudinal directions of the grooves 131 do notoverlap with each other. The reason thereof is as follows. If theextension lines extending in the longitudinal direction of the grooves131 of adjacent heating side lands 330 overlap with each other, there isfear that the solder flowing from the outlets of the grooves 131 facingeach other might harden, in a space between adjacent heating side lands330, in a state of sticking together at the time of the melting ofsolder. This could cause the short circuit in the heating side lands300.

Thin wire patterns for electrical connection 320 a (each of which isnumbered with 321 a, 322 a, 323 a, 324 a, 325 a, and 326 a) extend fromthe welding side lands 320 in the extending direction of the flexibleprinted circuit board 2 (the left-right direction in FIG. 5). Since thewelding side lands 320 are disposed in the zigzag pattern, the thin wirepatterns for electrical connection 321 a, 322 a, and 323 a, whichrespectively extend from the welding side lands 321, 322, and 323disposed on the side of the front end of the flexible printed circuitboard 2 (right side in FIG. 5), run close to adjacent welding side lands320 disposed on the side of the base end of the flexible printed circuitboard 2 (the left side in FIG. 5) or run between the welding side lands324, 325, and 326, without being electrically connected to the weldingside lands 324, 325, and 326. This configuration or arrangement of theheat side lands 330, the welding side lands 320 and thin wire patternsfor electrical connection 320 a increases the package density of theflexible printed circuit board 2, and thereby making it possible toreduce the width of the flexible printed circuit board 2 andconsequently to downsize the flexible printed circuit board 2.

The above advantages will become clearer through the comparison betweenthe present teaching and the following conventional example. Anexemplary flexible printed circuit board related to the conventionalexample is a flexible printed circuit board having comb-like electrode.This flexible printed circuit board is joined, with soldering via thecomb-like electrode, to counterpart electrodes connected to a straingage.

Each comb tooth of the comb-like electrode in this flexible printedcircuit board has a protrusion shape which is thin, long, and narrow.Thus, this flexible printed circuit board related to the conventionalexample is configured to have lands formed in the comb toothrespectively, and the pitch between adjacent electrodes cannot bereduced unlike the embodiment of the present teaching in which theflexible printed circuit board 2 has the heating side lands 330 and thewelding side lands 320 disposed in the zigzag pattern. Therefore, theconventional example still has the problem that the integration degreeof the flexible printed circuit board cannot be improved. The flexibleprinted circuit board 2 related to the present teaching, however, hasthe above configuration, which makes it possible to improve theintegration degree of the flexible printed circuit board andconsequently to downsize the flexible printed circuit board whileproviding the same number of electrodes as the flexible printed circuitboard related to the conventional example.

In addition to the above, since each tooth of the comb-like electrodehas the protrusion shape which is thin, long, and narrow, each tooth ismore likely to be bent or deformed. Thus, the comb-like electrode isrequired to be carefully handled so that no extra external force isapplied on the comb-like electrode at the time of solder joint. Theflexible printed circuit board related to the present teaching, however,does not have such a configuration, and thus handling thereof at thetime of solder joint is much easier than the conventional example.

The present teaching is not limited to the above embodiment, and theaction and effect of the present teaching can be also obtained throughthe following embodiments. For example, it is allowable to employ aheating side land 430 as depicted in FIG. 6B. The heating side land 430may have a circular or annular shape (doughnut shape) in which a hole435 is formed in the center to communicate with the through hole 140. Agroove (recess) 431 may be formed in the heating side land 430 so that apart of the heating side land 430 is left in its depth direction. Whenthe groove 431 is formed so that the depth of the groove 431 is smallerthan the height of the heating side land 430, a communicating hole isprovided on the bottom of the groove 431 to let the groove 431communicate with the through hole 140.

Instead of using the heating side land 130, of the above embodiment,which is formed of two semicircular plates and the groove 131 providedtherebetween, a heating side land having only one semicircular plate maybe used so that excess solder being melted is allowed to flow to an areaexcluding the semicircular plate of the heating side land. It is notindispensable to form the groove 131 over the entire area of thecircular plate-shaped heating side land 130 in its radial direction, asin the above embodiment. The groove 131 may be formed only in an areawhich ranges from the upper side opening of the through hole 140 to apoint on the outer circumference of the heating side land 130 (an areacorresponding to a radius of the circular plate). In this case, thegroove 131 may be formed so that the depth thereof reaches the bottom ofthe heating side land, like the above embodiment, or the groove 131 maybe formed so that a part of the heating side land is left in its depthdirection, like the modified embodiment.

As another modification, only one protrusion may be formed on the uppersurface of the heating side land of the conventional type which has aperfectly circular or annular shape and has the same height in itscircumferential direction. Alternatively, protrusions having the sameheight in its protruding direction may be formed on the upper surface ofthe heating side land in its circumferential direction.

Further, the height of the heating side land having the circular orannular shape may be periodically changed in its circumferentialdirection like a sine curve. Alternatively, steps having the same heightmay be periodically formed on the heating side land having the circularor annular shape in its circumferential direction. That is, the case, inwhich the heating side land includes a part having the perfectlycircular or annular shape (that is, a circular or annular shape of whichheight (thickness) is constant), may be also included in the scope ofthe present teaching, provided that the upper surface of the heatingside land against which the pulse heater is pressed has differentheights, unlike the heating side land related to the conventionalexample. In other words, any heating side land having a shape orstructure by which an air in a through hole can be released to theoutside of the heating side land, when a pulse heater is pressed againstthe heating side land, is included in the scope of the present teaching.

As described above, the recess related to the present teaching includesthe groove, which is formed to reach the bottom surface of the heatingside land (which is formed to penetrate the upper and bottom surfaces ofthe heating side land) so that the circular plate-shaped heating sideland is divided into two semicircular plates with a small space providedtherebetween. Further, for example, when a plurality of cylindricalprotrusions having the same height are provided around the upper sideopening of the through hole, and each of the protrusions and the weldingside land are thermally connected via a wiring extending from eachprotrusions to the through hole and a rolled copper foil in the throughhole, the recess related to the present teaching also includes gapsdefined between protrusions. That is, the recess related to the presentteaching includes various forms. Further, the heating side land 130 mayinclude a communication hole which connects the through hole 140 and theouter circumferential surface of the heating side land 130. That is, acommunication hole penetrating through a side wall of the heating sideland 130 may be provided at a position lower than the top of the heatingside land 130. In this specification, the “recess” and the“communication hole” described above are collectively called “a channelwhich connects the through hole and the outside of the heating side land(a first land)”.

More specifically, as is clear from the above embodiment in the presentdescription, the present teaching relates to the flexible printedcircuit board including, a flexible insulation layer having a firstsurface and a second surface, a first land which is conductive and whichis provided on the first surface of the flexible insulation layer, and aconductive member which is provided on the second surface of theflexible insulation layer, wherein a recess (groove) is formed on thefirst land. In this flexible printed circuit board, a through hole isformed in the flexible insulation layer, an edge of an opening, of thethrough hole, defined in the first surface of the flexible insulationlayer is in contact with the first land, and the recessfluid-communicates with the through hole and an outer circumferentialsurface of the first land. The present teaching, however, is not limitedto the above embodiment. As is clear from the modified embodiments inthe present description, the present teaching also includes theembodiment or aspect in which the recess is provided at a part of theperiphery of the opening of the through hole not to include theprotrusion constituting a part of the land, the embodiment or aspect inwhich the protrusion has a substantially semicircular shape in planview, and the embodiment or aspect in which the protrusions having thesame height are formed around the opening of the through hole at aregular interval in the circumferential direction of the opening of thethrough hole.

In the above embodiment, the counterpart electrode to which the flexibleprinted circuit board is connected is the electrode of the strain gage.The present teaching, however, is not limited to this. It is needless tosay that the electrode of the flexible printed circuit board related tothe present teaching can be reliably welded, with soldering, to thecounterpart electrode of any electric or electronic part.

Instead of providing the recess (groove) in the heating side land asdescribed above, the following configuration may be adopted. That is,the heating side land may be formed to have the circular or annularshape in which the upper surface thereof has the same height, like theconventional example. In this case, the pulse heater may be providedwith the recess (groove), which has a shape similar to the recess(groove) related to the above embodiment or the modified embodiments. Inthis configuration, melted solder is allowed to flow into the recess(groove) on the side of the pulse heater via the hole in the center ofthe circular-shaped heating side hand.

According to the embodiments of the present teaching, there can beprovided the flexible printed circuit board having the electrode, whichis connected or joined to the counterpart electrode via the solder jointwith sufficient strength so as to provide satisfactory conductivity fora long time.

What is claimed is:
 1. A flexible printed circuit board comprising: aninsulation layer which has a first surface and a second surface, and inwhich a through hole connecting the first surface and the second surfaceis formed; a metallic first land which is provided on the first surfaceand which is provided around an opening in the first surface defined bythe through hole; a metallic second land which is provided on the secondsurface and which is provided around an opening in the second surfacedefined by the through hole, the insulation layer being sandwiched bythe metallic first land and the metallic second land; and a metallicconnecting portion provided in the through hole to connect the metallicfirst land and the metallic second land, wherein a channel whichconnects the through hole and an outside of the metallic first land sothat the through hole and the outside of the metallic first land are influid communication with each other is formed at a position lower than atop of the metallic first land.
 2. The flexible printed circuit boardaccording to claim 1, wherein the metallic connecting portion isprovided on an inner circumferential surface of the through hole.
 3. Theflexible printed circuit board according to claim 2, wherein themetallic connecting portion is provided on an entire region of the innercircumferential surface of the through hole.
 4. The flexible printedcircuit board according to claim 1, wherein the metallic connectingportion covers a side surface of the insulation layer, the side surfacedefining the through hole.
 5. The flexible printed circuit boardaccording to claim 1, wherein the metallic first land is a disk-shapedmember which covers the through hole, and the channel is a slit whichextends in a radial direction of the disk shaped member and whichdivides the disk-shaped member into two parts.
 6. The flexible printedcircuit board according to claim 1, wherein the flexible printed circuitboard is a flexible printed circuit board to be soldered to acounterpart electrode with a heater, the top of the metallic first landis a contact surface to which a heating surface of the heater is broughtinto contact, and in a case that the heating surface of the heater is incontact with the contact surface of the metallic first land, an air inthe through hole is released to the outside of the metallic first landthrough the channel.
 7. The flexible printed circuit board according toclaim 1, wherein the channel is a groove.
 8. The flexible printedcircuit board according to claim 1, wherein a solder escape portion isprovided on a wiring connected to the metallic second land.
 9. Theflexible printed circuit board according to claim 1, wherein themetallic first land in which the channel is formed includes a pluralityof lands disposed in a zigzag pattern.
 10. The flexible printed circuitboard according to claim 9, wherein the channels of the lands are formedas grooves, and two lines respectively extending along longitudinaldirections of the grooves of two adjacent lands do not overlap with eachother.